Isoprene is the common name for the chemical compound known as 2-methyl-buta-1,3-diene, that is found in natural rubber. Isoprene is used as a starting material for the production of synthetic versions of natural rubber including polyisoprene and various isoprene-based rubbery copolymers such as styrene-butadiene type copolymers. Isoprene can be produced using a variety of processes. These can include, for example, byproducts of various refining operations such as the thermal cracking of naphtha or oil; the dehydrogenation of isoamylene compounds; the pyrolysis of allylic esters; and the decomposition of dioxane.
Isoamylene may be a component of a C5 refinery stream. The isoamylene portion of such a stream will typically contain at least two isoamylene monomers, i.e., 2-methyl-2-butene and 2-methyl-1-butene, often in a weight ratio of about 1:1 to about 10:1, and most often between 1:1 and 5:1, respectively. A third monomer, 3-methyl-1-butene may also be present but is typically in much lower amounts than the other two monomers. Isoprene can be produced by the catalytic dehydrogenation reaction of isoamylene in the presence of oxygen. The oxygen is typically provided by adding steam to the reaction zone.
N-pentene, also referred to as 1-pentene, is an alpha-olefin. N-Pentene is commonly made as a byproduct of catalytic or thermal cracking of petroleum, or during production of ethylene and propylene via thermal cracking of hydrocarbon fractions. N-pentene is rarely isolated as a separate compound. Instead, it is often blended into gasoline, or blended into a mixture with other hydrocarbons, which is alkylated with isobutane to make gasoline.
Piperylene, also known as 1,3-pentadiene, is commonly produced as part of the separation process when separating crude C5 compounds from pyrolysis gasoline. Piperylene may also be obtained from crude oil. However, obtaining piperylene from crude oil generally requires a number of extraction steps. Piperylene is used as an intermediate monomer in the manufacture of plastics, adhesives and resins. Products obtained from piperylene monomers are commonly present in adhesives, such as those used in the manufacture of tapes and envelopes.
N-butane, sometimes called simply “butane” is an unbranched alkane of four carbon atoms. N-butane gas is sold bottled as a fuel for cooking and camping. N-butane is also used as a petrol component and as a feedstock for the production of base petrochemicals in steam cracking. When n-butane is blended with propane and other hydrocarbons, it is referred to commercially as LPG.
Butadiene, also known as 1,3-butadiene, is a common monomer is the production of synthetic rubber. Butadiene is commonly produced as a by-product in the steam cracking processes used to produce ethylene and other olefins. Butadiene may also be produced by the dehydrogenation of n-butanes.
It may be desirable to utilize equipment that has the capability of producing more than a single product. For example, it may be beneficial to have the ability to utilize equipment typically used for the dehydrogenation of ethylbenzene to styrene also for the dehydrogenation of isoamylene to isoprene. It may be desirable to utilize commercial catalysts that are typically used for dehydrogenation reactions such as ethylbenzene to styrene reactions for the dehydrogenation of other hydrocarbons to alkenes, such as isoamylene to isoprene, pentene to piperylene, or n-butane to butadiene.
Efforts to utilize commercial catalysts that are typically used in ethylbenzene to styrene reactions for the dehydrogenation of isoamylene to isoprene have required high steam-to-hydrocarbon ratios and resulted in relatively short catalyst life. The higher steam-to-hydrocarbon ratio will increase the operating cost due to the need for more steam, therefore having an adverse effect on the economics of the process. Further, due to the decrease of catalyst activity, steaming of the catalyst is required in a regeneration step to restore activity. The operation of steaming the catalyst has a detrimental economic effect from the increased steam required and the reduction in product produced during this regeneration operation. The repeated action of steaming the catalyst typically results in a decrease in the useful life of the catalyst.
It may be desirable to be able to utilize equipment and catalysts typically used to dehydrogenate ethylbenzene to styrene also for the dehydrogenation of other hydrocarbons to alkenes, such as isoamylene to isoprene, n-pentene to piperylene and/or n-butane to butadiene in a method that exhibits increased catalyst life with a reduction in the need for catalyst steaming.